This invention relates to transducers for the transmission and reception of sonic energy and, more particularly, to a circuit permitting the connections of transmitting and receiving transducers by a single cable to a signal processing apparatus.
Transducers are utilized for the conversion of electrical signals to sonic energy, and the conversion of sonic energy back to electrical signals. While transducers are utilized in a wide variety of situations, one situation of particular interest involves the transmission and reception of sonic signals at very short range. Such a situation arises in the examination of objects, such as a metal pipe, to insure that such objects are properly constructed and free of any defects. For example, in the case of welded pipe, it is advantageous to check the pipe to insure that the weld is properly formed throughout the length of the pipe.
Considering the foregoing situation of the examination of an object, suitable test equipment for accomplishing such examination may be formed in the configuration of a radar system wherein a transmitting transducer and a receiving transducer are acoustically coupled to the exterior of the pipe. The transmitting transducer transmits a sonic wave into the metal pipe which reflects off of the weld and returns by the receiving transducer to a signal processor of the test equipment. In order to provide for good acoustic coupling between the transducers and the pipe, a pair of blocks of acoustic impedance-matching material such as Lucite blocks are advantageously positioned between the radiating surfaces of the transducers and the outer wall of the pipe. The blocks are shaped so as to mate with a wall of the pipe. Specifically, a short pulse signal is transmitted to the pipe. In order to attenuate any acoustic coupling between the two Lucite blocks, a sheet of sound-absorbing cork is disposed between the two blocks. The layer of cork enhances the quality of the received signal by reducing the coupling of any transmitted signal into the path of the received signal.
A problem arises in the use of such test equipment in that the round trip propagation time may be very much shorter than the duration of the test signal. Thus, a portion of the signal reflected from the weld may be received while a latter portion of the test signal is still being transmitted. As a result, two separate signal channels would normally be required for operation with the two transducers since temporal gating circuitry could not be employed in view of the simultaneous presence of the transmit and receive signals at the two transducers. However, in many tests situations, wherein numerous pairs of such transducers may be utilized in a test procedure, it is most desirable to simplify the equipment by employing a single cable for connection between the signal processor and the pair of transducers. However, such a single-cable arrangement is contraindicated in view of the foregoing necessity for two separate signal channels.